Lead-acid battery grid



Nov. 9, 1954 H. E. ZAHN LEAD-ACID BATTERY GRID Filed Nov. 21, 1952PLASTIC GRID I w G .1 F v FIG.5

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United States Patent Ofifice 2,694,099 Patented Nov. 9, 1954 LEAD-ACID 1BATTER GRID Harold'El Zahn, annals, N. Yyassi gnor to Gouid-NationalBatteries, 1110., St. Paul, Minn.

ApplicationNovemher21; 1952, Serial No; 321,765 8 {'Ilaimsr (GI?1236-58) This invention relates: toelectric'cell electrodes, and

more particularly to improved active'materialcontainers duction of asuccessful light weight battery is highly i desirable, for use. for;example for military purposes, efforts todate in this respect. have notproved: completely satisfactory. It. is of: course well: known that purelead and/or certain alloys thereof. are? sufliciently resistant tosulphuric acidand otherwise suitable as to indicate such materials tobe.the-most practicable for lead-acid storage battery grid constructionpurposes. However, such materials are so heavy that itis practicallyprohibitive to use solid lead or'lead alloys in the construction ofsuch. grids= wherelight weight is essential; and similarly in' alkalinebatteries the use of solid-nickel. and iron for=the grids, or nickel andcadmium, is highly disadvantageous-from: the weight standpoint. Ithasbeen suggested to fabricate: such i grids compositely soas tocompriseinner cores of;relatively'light weight material coated with outersheaths of metal to provide the requisite electrical conductivity andelectrolyte resistance throughout the; surface: areassin contact withthe battery electrolyte.

Thus, for example; as suggested in: U. S. Patent 1,509,186certainnon-metallic sheetsiof. relatively light weightfmaterial. havebeen punched into-the desired grid form and then given lead coatings-:byspraying molten metal upon thegrid structure,iand'/or* by. elctricaldeposition of lead. coatings upon such: corei supports; However, such priorart suggestions-have beeniunproductive of the desired results. In'thecase. of the: lead: spraying system the'product has been found. to betoo irregular and/or relatively porous atthe acid contact surfaces andthereby too fragile; to. provide: the: requisite degree ofreliability.Inthe case-of prior art: electro deposition methods employing anon-metallic base material and intermediateconductive coatingsof'graphite: or the like, it has been found that the'electro-plated:sheaf of. lead or leadalloy is quite thin and'relatively fragile-and. isrelatively insecurely attached. to: the core structure. tobe=practicable.- To avoid the aforesaid difliculties it has alsobeeniproposed to electro-plate theleadcoating'upon a lightiweightconductivecore'material'such as-a suitable aluminurnalloy; but suchefforts have failed to-producc uniformly satisfactory products becauseof the practical impossibility of: obtaining an electro-plated leadcoating of uniform thickness free. from zones" of weaknesssuch as arepenetrated by the-battery acid so'thatithe'latter thereby gains accessto the aluminum or other metallic core structure and thereuponproceeds-to leachzout the latter at rapid rate resulting in undercutting1 of the lead coating and complete disintegration of the-plate structure.

Whereas,- the'problem of. production of an improved light weight gridfor use in-alkaline batteriesistreated in my co filed patentapplication, it is the obiect of the present invention to provide an'-improved battery grid structure for. lead-acid batteriesv avoiding thevarious difiicultiesand disadvantagesreferred to hereinabove.

Another object of the invention is' toprovide: an iinproved light weightbatteryelectrode for. use in light weight lead-acid batteries, such asmay bereconomica'lly produced by modern large scale production shopprocesses.

Another object'of the inventionis to. provide anzimproved cellgrid-structureas aforesaid which will be of increased useful :longevity.

Still another object. of the invention is to provide in a composite cellgridoftthe type referred to improved electrical conductivitycharacteristics.

Othenobjects-and advantages-of the invention will ap= pear from thespecification hereinafter.

In the drawings:

Fig. lisa frontielevationals view of the core portion of a-lead-acidbattery; grid of the present' invention;

Fig. 2 is a fragmentary section, on anenlarged scale, of the coreconstruction of Fig; 1, taken along line II'Il of Fig; 1;

Fig.- 3 is. a view corresponding-to Fig. 2, but sub-' sequent toapplication thereto of an intermediate coating;

Fig. 4 is-a view corresponding to-Fig. 3, but illustrating a subsequentreplacement coating thereon; and

Fig. 5 is asimilarviewshowing application over the structure ofFig. 4 ofa1. finalleadcoating, thereby illustratingatypicaLsectional view throughany portion of the finished grid structure;

The present:inventionacontemplates abattery cellplate grid forlead-acidtype batteries: comprising a novel composite structureconsisting: of a: relatively light weight core element whichisalso-highly resistant to battery acid; a'sub-co'atingtof relativelyhigh conductivity metal coveringthegrid core? element; and an'outercoating oflead or lead alloy sodeposited-over the sub-coating asto-provide'the active pastevcontacting portions of the grid structure.More specifically, .the outer lead or lead alloy coating is-sodistributed over the'sub-coating so asto provide: thereover. a:uniformly dense and acidresistant armori; but. it is a particular:feature of the present invention that in event the battery acid happensto.- workthrough the lead coating portion of the grid it simplydead-ends against the: acid resistant plastic core material, wherebyundermining of the metallic coating; portions of the structure anddisintegration thereof are avoided.

For example, as shown: inthe drawing, a grid struc tureof. theinventionsmay be. fabricated by initially in jeotion-molding or strikingout of a sheet of suitable plastic material a. gridcorestructure'asindicated generally at 10, as by any suitable molding orstamping or die cutting. process: or thelike such as would be obvious toanyone-skilled in Y the art. The-material from which the grid structure19 is formed may comprise suitable. acid-resistant and relatively lightweight plastic material such as selected for example from thepolystyrene group; orthe polyethylene group; and in either case theplastic material may be ofeither the electrically conductive ornonconductive' type. In this respect references made tothe fact thatwhereas plastic materials=are ordinarily electrically nonconductive,they may; be manufactured to include graphitic or metallic fillers or.the-like soas-torender them electrically conductive; and one specific.example of such a material that is-suitable forthis:purpose'is-presently commercially available under the tradenarne.l\ iarkite'. It is to be understood: that in event a plasticmaterial of the socalled conductive typeis employed, the core structureper sewill-contribute to the overall electrical conductivity of thefinished product which includes the relatively highly conductive.metallic .su b-coating layer under the corrosionresistant. outsidematerial layer.

In any-case the gridltl will be sothickness dimensioned as to allow forsubsequent coating thereof, as will be explained. hereinafter, toprovide the overall desired thickness of the finishedgrid structure'. Itwill. of course be understoodrthat the grid core structure it may be ofany preferred profile configuration, and will be designed. so as toprovidev the active paste carrying pocket. formations of. the desiredshape and dimensions. asis customary in the art. Thus, for exampleas-shown in the drawing, the grid core structure may include a terminalportion 12:.a top bus bar portion 14; vertical ribs 16': and horizontalribs 18;.the vertical and horizontal rib formations? cooperating toprovide the active paste receiving pocket portions of the grid, as isWell known in the art; Thus, a fragmentaryv sectional view ofthe I =3grid core structure will appear as illustrated at Fig. 2 in the drawing.

The invention involves placement of an undercoating of relatively highconductivity metal on the plastic core; such as an undercoating of tinor copper or silver. If an undercoat of silver is desired the next stepin the process of the invention may involve temporarily wetting theplastic core structure with a Water solution of stannous chloride, as bya dipping or spraying operation so that the plastic core piece isthoroughly wetted with the stannous chloride solution, as indicated at20, Fig. 3. Then the next step in the process of the invention is toprocure a replacement of the tin elements of the core coating withsilver so as to provide an undercoat of pure silver over the plasticcore structure, as indicated at 22 in Fig. 4. This replacement of thetin by silver may be accomplished either by dipping the stannouschloride wetted core piece in a water solution of silver nitrate, or byfirst coating the core piece with graphite and then submerging it in asilver electroplating bath. In either case the obiective is to replacethe tin by a pure silver coating of the order of 710mm) of an inchthick. Then as the third step of the process of the invention the silverplated core piece is transferred to a lead plating bath whereupon a leador lead alloy coating as indicated at 24 (Fig. 5) is applied over thesilver undercoat 22. In the event that an electrically conductingplastic of the type above mentioned is used for the plastic core thehigh conductivity metal undercoating might be p aced thereon by directelectrodeposit without prior c nditioning, as by stannous chloride; orif functional life and capacity demands permit. the undercoating mightbe eliminated entirely and the lead coating would then be directlyapplied to the plastic core piece.

The grid structure is then prepared for reception of active pastematerial in the pockets thereof, as is well known in the art; and itwill of course be appreciated that when the grid is pasted the activepaste material will come in direct contact only with the outer lead coating '24 and that the battery acid will have access only to the outerlead coating. At the same time, it will be appreciated that whereas theconductivity of the lead coating is rather low, the battery currentswill flow readily through the lead coating and into the silvernndercoating and thence toward the grid terminal with greatly improvedfacility compared to a correspondingly dimensioned grid structure of theprior art. At the same time, due to the fact that the core element ofthe grid structure is of light weight plastic material, the overallweight of the grid structure is greatly reduced compared tocorrespondingly dimensioned grids of the prior art.

Thus, the combination lead and silver coating structure of the gridmember provides improved conductivity characteristics compared to asolid lead structure of equal sectional thickness without beingexcessively expensive from the standpoint of cost and materials and/orfabrication: and furthermore the relatively fragile low tensile strengthlead material of the outer coating of the grid structure of the presentinvention is thereby structurally bonded to the relatively strongersilver undercoat and thereby to the extremely tough plastic core elementof the structure. thereby providing a novel composite grid structurewhich is of greatly improved overall strength and resistance a ainstphysical disrupture due to vibration or shock. In this respect it willbe appreciated that the composite novel grid structure of the presentinvention possesses an overall phvsical strength greatly superior tothat of a solid lead grid for example. which is notoriously weak andsubiect to ph sical failure under vibration or shock, as well as beinexcessively heavy and therefore impracticable for certain uses.

It is another particular feature and advantage of the grid structure ofthe present invention that in event of any imperfection in the leadouter coating portion 24 thereof, whereby battery acid sim ly reaches adead end because the silver layer undercoat is too thin to permitundercutting by the battery acid between the lead outer coat and theplastic core, and because the plastic core element is completelyacid-resistant. Consequently, undercutting of the lead outer coat isefiectively forestalled and introduces no problem of grid disintegrationsuch as has been experienced in attempts to provide a lead coatedaluminum core type grid, or the like. Thus, it will be appreciated thata relatively thin layer of lead material provides, in the case of thepresent invention, a perfectly adequate armor against the battery acid;whereby an extremely light weight yet adequately armored grid isprovided. Also, it will be appreciated that the composite grid structureof the present invention is of reduced resistance to electrical currentflow, for any given lead sectional thickness; and because of thesuperior conductivity characteristics of the composite grid structure ofthe invention a maximum volume of active material may be supported in aminimum volume of support frame.

Whereas the invention has been described in detail hereinabove inconnection with a lead-acid storage battery grid construction whereinthe undercoat is formed of silver deposited on the core structurethrough replacement of a temporary tin salt coating; it is to beunderstood that the invention may be practiced in various modifiedforms. For example, in lieu of the use of a stannous chloride dippingmethod as explained hereinabove, the initial tin coating may be suppliedby direct vapor deposition of pure tin on the plastic core structure, orby electro-plating the tin thereon. Also, it is to be understood that inlieu of the silver undercoat as described in detail hereinabove, asatisfactory permanent undercoat material may comprise either tin orcopper; and that in any case the undercoating metal may be plated overthe plastic core structure by any suitable method such as vapordeposition or electro-plating or some suitable chemical replacementprocess. In any case the relatively high conductivity undercoat metalwill be subsequently outer-coated with lead or lead alloy, as explainedhereinabove, so as to provide suitable acid insulation of the relativelyhigh conductivity undercoat metal.

Thus, it will be appreciated that although only a few forms of theinvention have been illustrated and described in detail, it will beapparent to those skilled in the art that the invention is not solimited but that various changes may be made therein without departingfrom the spirit of the invention or the scope of the appended claims.

I claim:

1. In a battery, a grid comprising a core formed of an acid-resistantplastic material having a first coat of high electrical conductivitymetal thereon and an overcoat of lead thereon.

2. In a battery, a grid including a core formed of an acid-resistantplastic material undercoated with electrically high conductivity metaland overcoated with lead, the pocket formations of said grid beingfilled with battery active paste material.

3. In a battery, a cell plate having a terminal and comprising a coreformed of an acid-resistant electricallyconductive plastic materialhaving bonded thereon a relatively thin lead coating, said plate havingan electrically conductive path from said coating to said terminal, saidpath comprising said plastic material.

4. An improved lead-acid battery grid construction, comprising acompositely formed grid including a core piece of grid configurationformed of an acid-resistant plastic material, said grid having thereon asub-coating of relatively high electrical conductivity metal and anouter coating of relatively lower electrical conductivity butacid-resistant metal, whereby corrosive action of the batteryelectrolyte against said battery gridconstruction is substantiallyforestalled.

5. A battery cell plate grid compositely formed from a core ofacid-resistant plastic material pocketed to receive battery active pastematerial therein, said grid being uniformly coated with two bondedmetallic layers, the undercoat layer being of a relatively highelectrical conductivity metal selected from the class of metalsincluding silver, tin and copper, and the outercoat layer being of anacidresistant metal such as lead or lead alloy.

6. An improved lead-acid battery grid construction, comprising acompositely formed grid including a core piece of grid configurationformed of an acid-resistant plastic material, said grid having thereon asub-coating of silver in the order of 7 of an inch thick and an outercoating of relatively lower electrical conductivity but acid-resistantmetal, whereby corrosive action of the battery electrolyte against saidbattery grid construction is substantially forestalled.

7. A method of making an electrically conductive and acid-resistantbattery cell plate grid by forming a plastic material into cell-plategrid shape, coating said plastic with a water solution of stannouschloride and then reacting said stannous chloride with a Water solutionof silver nitrate whereby the said plastic material receives a bondedcoating of silver in the order of 4 of an inch thick and subsequentlyovercoating said silver coating by a layer of metal selected from thegroup including lead and lead alloys by means of electroplating.

8. A method of making an electrically conductive and acid-resistantbattery cell plate grid by forming a plastic 10 material selected fromthe group including polystyrene and polyethylene plastics intocell-plate grid shape, coating said plastic with a water solution ofstannous chloride and then reacting said stannous chloride with a Watersolution of silver nitrate whereby the said plastic material receives abonded coating of silver in the order of A of an inch thick andsubsequently overcoating said silver coating by a layer of lead by meansof electroplating.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,639,280 Benner et a1. Aug. 16, 1927 2,190,121 MisciatelliFeb. 13, 1940

1. IN A BATTERY, A GRID COMPRISING A CORE FORMED OF AN ACID-RESISTANTPLASTIC MATERIAL HAVING A FIRST COAT OF HIGH ELECTRICAL CONDUCTIVITYMETAL THEREON AND AN OVERCOAT OF LEAD THEREON.